The present invention relates to a process for detecting the occurrence of corrosion in steam turbine installations during the operation of the latter, and to a device for carrying out the process.
When operating steam power stations supplied with steam generated from fossil or nuclear fuel, optimum availability of the installation is desired, coupled with the lowest possible fuel consumption. The aggressive impurities present in the steam, which are separated out with the first condensate, can cause corrosion in the circulation system and hence lead to material damage in the turbine and to detrimental oxide deposits in the heat exchangers. In addition to this corrosive damage, chemical destruction also occurs on materials which are mechanically stressed; for example, stress corrosion cracking, fatigue corrosion, vibration corrosion at the like.
Since the impurities responsible for damage of this type and chemical substances contained in the steam are present only in very small amounts and concentrations, a direct detection of such substances is possible only at great cost even if the most modern analytical techniques are used. Even the fitting of corrosion test pieces in the turbine does not give the desired result since the zone in which the first condensate is formed is very narrow and its exact position depends on various factors, such as load, cooling water temperature and the like. Moreover, observation of corrosion test pieces of this type during operation of the installation is possible only by using expensive apparatus.
It is, therefore, an object of the present invention to develop a process which detects corrosion in the installation during the operation of the latter, and to provide a device with which a measurement of the aggressivity of the working medium can be carried out continuously.
According to the present invention, the object stated above, and others, are achieved by the following process steps:
(a) working medium in the superheated state is taken from the steam circulation and partially condensed by cooling,
(b) the condensate is separated from the remaining steam, after which the quantity of condensate and the quantity of remaining steam are determined,
(c) the remaining steam is returned as steam or, after complete condensation, as water into the circulation, and
(d) the condensate is continuously examined for its corrosivity or agressivity.
Advantageously, the working medium is measured optically for the purpose of quantitative control of the condensation step; at most, 2% of the working medium should be condensed.
The working medium is sampled directly from the steam circulation and only a small part, namely, at most, 2%, but preferably less than 1%, is condensed. The aggressive impurities are present in this condensate in a correspondingly concentrated form, and their aggressivity can be monitored continuously.
According to an advantageous process step, a metal test piece is exposed to the condensate in order to detect aggressivity. Since the condensate which is to be examined contains all the impurities present in the working medium in a concentrated form, the aggressivity and the corrosive action of the impurities can be detected earlier on these metal test pieces, around which the condensate flows, than the aggressivity and corrosive action of the impurities can be detected on metal parts of the turbine installation under attack.
According to another advantageous process step, the condensate is further cooled to a suitable temperature and subjected to chemical and physical analysis.
Cooling the condensate and passing it through various measuring cells permits the determination of different parameters to be measured parallel to one another. This procedure makes it possible to continuously recognize impurities which represent a potential risk to the materials in the thermal circulation, with sufficient time to take remedial measures.
The measuring device for carrying out the process according to the present invention essentially comprises a condenser, a water separator, two flow meters and a test apparatus, all of which can be connected to a steam sampling point on the installation.
The condenser cools the steam and hence forms a first condensate which is separated from the remaining steam in a water separator. The condensate is then passed to a test apparatus where, corresponding to the requirements, aggressivity tests on the noxious materials contained in the condensate and/or further chemical and physical analyses can be carried out.